X-ray imaging systems may be utilized for various applications both in a medical and in a non-medical field. For example, medical X-ray imaging systems may include general radiological, mammography, X-ray C-arm, tomosynthesis and computed tomography imaging systems. Such imaging systems may be adapted to create images or views of a part of a patient based on an attenuation of X-rays passing through the patient. Alternatively, X-ray imaging systems may be used in non-medical applications such as security screening of passenger luggage or industrial quality control.
In the following, one specific application of X-ray imaging known as tomosynthesis which may be used for example in medical X-ray mammography analysis will be described in more detail. However, it is to be noted that the present invention is not limited to such application.
In tomosynthesis multiple X-ray projections may be taken of a same region of interest, but from different angles, in order to provide volumetric (3D) or quasi-volumetric (quasi-3D) information of the imaged object after a mathematical reconstruction process of acquired image data. Generally, with tomosynthesis, a total angular range of an acquired data set is limited. This may mean that not a full 3D reconstruction of the region of interest can be obtained but a depth resolution may be much lower than a 2D resolution of originally acquired individual X-ray projections, and it may depend on the number of X-ray projections and the total angular range for which X-ray projections have been acquired.
A conventional system setup for X-ray tomosynthesis for medical imaging comprises a conventional X-ray tube that is sequentially moved to different locations, taking a projection image of the same region of interest at each location with a detector positioned on an opposite site of the object. A path described by the X-ray tube may be straight, a circular segment or any other curve within a limited total angular range. The X-ray tube used in such conventional system setup for X-ray tomosynthesis may usually be a standard X-ray tube with a rotating anode because a maximum possible power rating of a an X-ray tube with a stationary anode may not be high enough in order to obtain a required number of images within a given period of time, e.g. within several seconds.
However, a standard X-ray tube with a rotating anode, as it is used e.g. for mammography, may be very large and heavy. Therefore, it may be very difficult to move such X-ray tube through a number of different image acquiring locations. Two approaches are generally pursued, however each with its own disadvantages:
(a) step and shoot: This may require frequent and rapid acceleration and deceleration of the entire X-ray tube, which might lead to vibration of the total X-ray imaging system, possibly deteriorating an image quality due to motion artefacts;
(b) continuously moving the X-ray tube: The moving X-ray source (and therefore the continuously moving focal spot) may blur the acquired X-ray projection images.
In any of these cases, it may not be possible to move the large and heavy X-ray tube very fast such that a total examination time may be quite long. In case of tomosynthesis for mammography this may result in considerable patient discomfort in addition to a risk of generating motion artefacts for example due to breathing.
If, as an alternative, multiple stationary X-ray tubes were used instead of a single moving X-ray tube, standard rotating anode tubes might be too large to be mounted side by side. Also, a resulting power consumption and cost price of such system might be too high for a commercial medical imaging system.
As a further alternative, small conventional X-ray tubes with a stationary anode might be used. However, in such X-ray imaging system, required power rating might not be reached in order to obtain a required number of images within a reasonably short time.
Again, a long total examination time may lead to considerable patient discomfort.